Protection from creatures prevents targeting with Bloodrush.

To quickly remind yourself of what protection does, just think of the Orzhov guild’s favorite word: DEBT. D stands for dealing damage; E stands for enchanting/equipping; B stands for blocking; and T stands for targeting.

While you might be most familiar with protection from a color, protection can also encompass a wide variety of other things. For example, Holy Mantle gives “protection from creatures.” If we apply this quality to the four letters of DEBT, we learn that our protected creature can’t be dealt damage by creatures; it can’t be equipped or enchanted by creatures (not that it could, anyway); it can’t be blocked by creatures (in other words, not at all); and it can’t be the target of abilities of creatures.

But what does this all have to do with Bloodrush? After all, the word “creatures” usually refers to creature permanents on the battlefield (for example, your Glorious Charge won’t increase the power of that Slitherhead in your graveyard). Here’s another wrinkle: protection has an exception that makes it apply not just to permanents, but to all cards and spells not on the battlefield which have the chosen quality. So a creature geared up with Holy Mantle can’t be the target of a Bloodrush ability, because its source has the word “Creature” in its type line. It can’t be scavenged onto by Slitherhead, either.